The present invention relates to a device mounting a semiconductor element such as a pressure sensor or a large semiconductor where the semiconductor element should strongly adhere to the substrate on which it is mounted.
A conventional device mounting an integrated circuit, semiconductor element or the like is depicted as device 31 in FIG. 1. Such a device comprises a ceramic substrate 34 on which is mounted a semiconductor element 33 by means of a joining layer 32 which is normally comprised of a metalized or plated layer on the substrate. A cap 35 is mounted by means of a glass layer 36 in such a manner that it protects the semiconductor element 33. The glass layer 36 provides a gas-tight seal between the ceramic substrate 34 and the cap 35. Terminal members 37 extend through the glass layer 36 from the outside of the device to a position adjacent the semiconductor element and are electrically connected thereto by means of electrical conductors.
Normally, the material used to form the ceramic substrate 34 is alumina or mullite which provide the requisite mechanical strength and electrical insulation characteristics. It should be noted, however, that the substrate on which the semiconductor element is mounted has a thermal expansion coefficient of 80.times.10.sup.-7 /.degree.C. for alumina and 45.times.10.sup.-7 /.degree.C. for mullite, while the semiconductor element which normally consists of silicon that has a coefficient of thermal expansion of 25.times.10.sup.-7 /.degree.C. Therefore, when a large semiconductor element is mounted on such a substrate, thermal strain caused by differential thermal expansion between the two components during the joining operation decreases the yield and the durability of such a device. This is especially true when the device is used as a pressure sensor having a metal substrate because it may be cracked during its use at high temperatures.
Accordingly, there has been a strong demand for a device mounting a semiconductor element which is heat resistant, gas tight, and durable when subjected to vibration and which can be produced at a high yield at a low manufacturing cost.
Accordingly, it is an object of this invention to eliminate the above-described difficulties accompanying conventional devices of this type.